The present invention relates to equipment for recovery of liquid tank cargo from a vessel at sea, such as a tanker having an oil cargo, in the case of a leakage, for instance by running aground.
It has shown to be nearly impossible to prevent a disaster when oil leaks from a tanker, when the leakage itself cannot be stopped. Recovery of the oil that has leaked out has shown to be little efficient.
The invention is premised upon the inefficient recovery of the leaked oil which has been attempted and the appreciation that the problem can be attacked in a substantially different manner, by limiting the leakage itself substantially.
This is achieved with the equipment according to the invention, which constitutes stand-by equipment to be used as immediately as possible after leakage from a tanker has been discovered, in order to limit as far as possible the quantity of leaking oil.
Oil is usually transported in tankers in such a manner that the oil level in the tanks of the vessel is higher than the water level outside the vessel. Moreover, an excess pressure is usually established by means of an inert gas above the oil, in order to prevent evaporation of oil. Thus, if the formation of a hole occurs in the bottom of the vessel, oil will be forced out because of the excess static pressure of the oil relative to the static pressure of the water surrounding the vessel, and the excess pressure of the gas above the oil will contribute to increase the leakage of oil. If nothing is done to prevent the leakage, except that the excess pressure may come to an end when the volume of the free space above the oil increases due to the leakage, the leakage may continue until a static equilibrium between the remaining oil in the vessel and the surrounding sea water has been established. By the time such an equilibrium occurs very large quantities of oil may have leaked out, and a disaster will usually be a fact, even if attempts of recovering the oil from the sea are made.
The primary purpose of the equipment according to the present invention is to stop the leakage itself, by as quickly as possible to pumping oil out of the vessel or from the tank or tanks of the vessel from which leakage occurs, whereby the oil is collected in a container which is carried along or stored in a collapsed state and which in a case of leakage is placed in the sea, whereupon oil is pumped from the vessel and into the container.
Preferably a low pressure is established in the free space of the vessel above the leaking oil, in order to limit the outflow of oil. The pumping of oil to the container floating in the sea is, however, most important, in order to reduce the oil level inside the vessel so that the static excess pressure of the oil relative to the static pressure of the sea water in the leakage area diminishes and preferably is eliminated or becomes so small that continued leakage can be prevented by the low pressure.
The collapsed container, which may for instance lie on the deck of the vessel, can be permanently coupled to a hose connected to a pump in the vessel. The hose can be wound on a drum, and the collapsed container, which can be made of a fabric, may for instance be stored on some kind of a catapult device, in order to be hurled onto the sea.
A pump for establishing low pressure above the leaking oil may also be permanently connected and ready for use.
The equipment according to the present invention can also constitute a mobile unit which comprises a collapsible fabric container and a hose being wound on a drum and coupled to the container, whereby the container in a collapsed condition is releasably fastened to a stand in which the drum is journalled.
Moreover, the unit may comprise another drum with a hose adapted to be introduced in a leaking tank in a vessel, and the two hoses may be coupled together. A pump may be interposed between the two hoses.
Such a mobile unit (or several) according to the invention can be permanently situated aboard a vessel, but the most important use is assumed to be that several units are placed on land, preferably in coastal areas, in order that they may be carried by helicopters or seagoing vessels to a leaking vessel. After having been brought to the vessel the unit is made ready for use, in that the fabric container is hurled onto the sea, the stand is placed on a deck on the vessel and the hose being coupled to the container is brought in communication with the leaking tank in order to pump oil into the fabric container.
In order to be efficient the fabric container must have a large volumetric capacity, but the capacity will in practice be limited by the total weight of the unit in its stand-by condition, depending on how the unit is to be transported, when it is assumed that it is situated on land. For transportation by helicopter the weight should presumably be limited to about 3 tons, and this is supposed to permit a volumetric capacity of the fabric container of up to about 10.000 m.sup.3. For transportation by seagoing vessels the limit is of course substantially higher.
In order to prevent the container, when lying in the sea and receiving oil from a leaking vessel, from drifting away so that the hose for transfer of oil is torn apart, it may be necessary to moor the container to the vessel. The unit may for this purpose also conveniently comprise a third drum carrying a mooring line. In the stand-by condition the container in a collapsed state may simply be fastened to the stand by suitable means, but preferably in such a manner that the container can be released from the stand while the stand is hanging below a helicopter. It may for instance incorporate strap fasteners which can be released from the helicopter. The container may, however, be situated in some kind of a cover, for instance a bag or a box. The bag may for instance have an opening in the bottom which is closed during storage and transportation and which can be opened from the helicopter in order to be dropped onto the sea, for instance by cord release. Correspondingly the box may have a lid which can be opened from the helicopter, or the box may be open along one side or end, for pulling out the container.
The invention will be explained more detailed in the following, by means of diagrammatically shown examples, with reference to the accompanying drawings.